The present invention relates to an acoustic diaphragm formed of beryllium or an alloy composed mainly of beryllium, which is best suited for use in moderate and high-frequency regions.
In the prior art, materials having a high Young's modulus E and a low density .rho., say, a high E/.rho. ratio have been found to be best suited for use in acoustic diaphragms.
However, beryllium or an alloy composed mainly of beryllium is brittle and shows poor ductility and processability, so that its pressing or rolling at room temperature is practically impossible.
To this end, such a type of diaphragm has been prepared by means of hot-rolling, hot-pressing or vacuum deposition.
Of these means, hot-pressing or hot-rolling involves a first step of finely chipping (B) a beryllium ingot (A), a second step of pulverizing (C) the resulting chips into a particle size of not more than 200 mesh followed by sieving (D), and a third step of finely pulverizing the resulting particles to form powdery beryllium, as shown in FIG. 1. In a further or fourth step, the powdery beryllium is subjected to vacuum hot-pressing to form a hot-pressed block (F). The block F is sandwiched between plates of, e.g., stainless steel, and welded together on its circumference. In a subsequent or fifth step, hot-rolling (G) is repeated until the product having a desired thickness is obtained.